Photovoltaic Cells: Solar Cells

EBB 424

Dr. Sabar D. HutagalungUSM

Efficiency Efficiency = Fraction of incident light energy converted to electrical

energy. Efficiency is the most important characteristic because it allows the

device to be assessed economically in comparison to other energy devices.

For a given solar spectrum, the efficiency depends on: Semiconductor material Device structure Ambient conditions (temperature) High radiation damage Sun spectrum

Efficiency alone is not enough, the cost of the cell is also important and the life time.

I-V characteristics & Efficiency

Typical I-V characteristic of solar cells

in dark (diode)

under illumination

As the intensity increases, the short-circuit current ISC increases linearly, but the open circuit voltage VOC increases sublinearly.

I-V characteristics & Efficiency

The I-V characteristics of a solar cell with varying illumination as a parameter.

I-V characteristics & Efficiency

The I-Va characteristic of a solar cell. The maximum power is obtained at Pm ImVm

I-V characteristics & Efficiency

(I)(II)

(III) (IV)

I-V characteristics & Efficiency

I-V characteristics & Efficiency

I-V characteristics & Efficiency

The I-V characteristics of a solar cell with varying illumination

I-V characteristics & Efficiency

Calculation, Consider a solar cell driving a 30 resistive load. The cell has area = 1 cm x 1 cm and is illuminated with light of intensity = 600Wm-2 and has I-V characteristic as shown below.

Q: What are the current and voltage in the circuit?

A: I’ = 14.2mA , V’ = 0.425V

Q: Calculate the power delivered to the load (Pout)

A: Area under the I’, V’ rectangular = P

P= 14.2 x 10-3A x 0.425V = 6.035mW

14.2mA

0.425V

Calculation,

Q: Calculate the input sun-light power

A: Pin = (light intensity x surface area)

Pin = 600Wm-2 x (0.01m)2 = 0.06W

Q: Calculate the efficiency of the device

A: = 100x (Pout/Pin)

Pin = 0.06W

Pout = 6.035mW

= 10.06%

Q: State why the efficiency is very small?

Solar Spectrum

Conversion Efficiency

The most efficient PV modules usually employ single-crystal Si cells, with efficiencies up to 15%.

Poly-crystalline cells are less expensive to manufacture but yield module efficiencies of about 11%.

Thin-film cells are less expensive still, but give efficiencies to about 8% and suffer greater losses from deterioration.

Solar Photovoltaic Plants

How PV Cells Work

Diagram of a photovoltaic cell

Photovoltaic cells, modules, panels and arrays

Major photovoltaic system components.

18

Problem

Suppose that a particular family house in a sunny geographic location consumes a daily average electrical power of 1500 W supply by an 50 m2 are of solar panel. The average solar intensity incident per day is about 6 kWh m-2. What is the efficiency of solar cell?

19

Solution

Total sunlight energy per day: = intensity x area

= 6 kWh m-2 x 50 m2= 300 kWh

Solar cell output = 1.5 kW x 24 h = 36 kWh

Efficiency = Output/Total energy light= 36 kWh/300 kWh= 12 %

Solar Cells